• Clemens Ladisch's avatar
    ALSA: pcm: fix delta calculation at boundary wraparound · b406e610
    Clemens Ladisch authored
    
    
    In the cleanup of the hw_ptr update functions in 2.6.33, the calculation
    of the delta value was changed to use the modulo operator to protect
    against a negative difference due to the pointer wrapping around at the
    boundary.
    
    However, the ptr variables are unsigned, so a negative difference would
    result in the two complement's value which has no relation to the actual
    difference relative to the boundary; the result is typically some value
    near LONG_MAX-boundary.  Furthermore, even if the modulo operation would
    be done with signed types, the result of a negative dividend could be
    negative.
    
    The invalid delta value is then caught by the following checks, but this
    means that the pointer update is ignored.
    
    To fix this, use a range check as in the other pointer calculations.
    Signed-off-by: default avatarClemens Ladisch <clemens@ladisch.de>
    Cc: <stable@kernel.org>
    Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
    b406e610
pcm_lib.c 58.4 KB